Throttles are widely used in many fields, e.g. in throttle valves, and can comprise a housing containing a throttle cage or body interposed in a flow path of the fluid to be throttled.
Such throttles can be employed, for example, in the chemical industry in a wide variety of chemical processes, in oil fields and, in general, in many applications in which the throttle body is subjected to stress.
Thus stresses can be, for example, pressure stresses, thermal stresses and the like which alternate between periods of high and periods of low temperature and/or pressure stress (alternating stresses).
The throttle body can be formed with openings which not only constrict the fluid flow in the throttling action but provide an energy-dissipative action, i.e. allow streams of the fluid to impinge upon one another to dissipate the energy of such streams.
In addition to the alternating stresses to which the throttle body is made subject, it can be subjected to a variety of mechanical and chemical stresses which can cause deterioration including cavitation stresses, corrosion stresses and abrasive actions. In chemical process technology and in oil field use, substantially all of the aforementioned stresses are applicable at substantially all times. The fluid which is throttled can be a liquid, a gas, a vapor and a chemically corrosive substance or a fluid entraining mechanically abrasive or chemically corrosive material.
In the past, the throttle body, formed as a throttle cage, i.e. a sleeve or tubular member having radial passages which constitute the throttle passages, was usually composed of a steel alloy of a specific composition determined by the processes to which the throttle cage might be subjected. Notwithstanding the selection of a steel composition which was intended to resist deterioration, the life of the throttle body was limited. Indeed, steel compositions which can provide the desired length of the useful life are not available.
While it has been proposed to make the throttle body of an engineering ceramic, here too the life could not be satisfactorily increased because the ceramic structures had limited ability to withstand the shock stresses of a thermodynamic type in both a gas-dynamic or hydrodynamic environment. Although such bodies could withstand abrasion and many types of corrosion, when they were subjected to thermal and mechanical shock, they were less than adequate. Indeed, in many fields ceramic valves or the like have been provided and have a long useful life as long as the stresses to which the valve elements are subjected are less complex and varied than those of the throttle systems with which the present invention is concerned.